1. Field of the Invention
The present invention relates to an ultrasonic operation apparatus which can detect an abnormality, and an abnormality judgment method of the ultrasonic operation apparatus.
2. Description of the Related Art
Conventionally, an ultrasonic operation apparatus, such as an ultrasonic coagulation/incision apparatus or the like, for giving a treatment to a target to be treated with ultrasonic waves is used. Such an ultrasonic operation apparatus comprises an apparatus main body which generates a drive signal. To the apparatus main body, a hand piece (also called a hand instrument) is connected. This hand piece accommodates an ultrasonic transducer, to which the drive signal is input and which generates ultrasonic vibrations. To the hand piece, also the base of a probe which conveys the ultrasonic vibrations is connected. With the tip of the probe, a treatment is given to a target to be treated with the ultrasonic vibrations conveyed from the base of the probe to its tip.
Such an ultrasonic operation apparatus can increase the efficiency of a treatment by driving the hand piece at its resonance frequency. Here, a drive frequency at which a phase difference between an output voltage and an output current to the hand piece becomes 0 is the resonance frequency. In the ultrasonic operation apparatus, a PLL (Phase Locked Loop) control for controlling the drive signal is performed so that the phase difference between the output voltage and the output current becomes 0.
In the meantime, since a treatment is given by pressing the probe, which makes ultrasonic vibrations, against a target to be treated in the ultrasonic operation apparatus, a blade, etc. attached to the tip of the probe sometimes gets loose during the treatment, or a mechanical degradation can occur in the probe or the hand piece by continually applying a mechanical stress which occurs with the ultrasonic vibrations.
One example of the ultrasonic operation apparatus which can detect such abnormalities is disclosed by Patent Document 1. The ultrasonic operation apparatus of Patent Document 1 detects abnormalities such as a break, a crack, a blemish and the like of a probe. Namely, when an abnormality occurs in the probe, an abnormality is judged to occur in the probe when a resonance frequency changes from its normal value, namely, when the resonance frequency calculated under a PLL control goes out of a predetermined range. If the abnormality is judged to occur, an output to the hand piece is suspended, and the abnormality is notified with sound, light, vibrations or the like.
Similarly, an ultrasonic operation apparatus of Patent Document 2 records a resonance frequency in an early stage, and judges that an abnormality occurs in a probe or a hand piece if the resonance frequency changes from that in the early stage by a predetermined value or more.
Furthermore, an ultrasonic operation apparatus of Patent Document 3 obtains a frequency deviation, which is a difference between a prerecorded setting frequency and a calculated resonance frequency, and judges that an abnormality occurs in a probe or a hand piece if the frequency deviation goes out of a predetermined monitoring frequency range.
Still further, an ultrasonic converter of Patent Document 4 judges that an abnormality occurs in a probe or a hand piece if a calculated resonance frequency goes out of a predetermined resonance point tracking range.
Patent Documents 5 and 6 disclose ultrasonic operation systems which judge an abnormality separately from a PLL control. The ultrasonic operation system of Patent Document 5 detects the looseness of a blade attached to the tip of a probe. Namely, this ultrasonic operation system can calculate impedance from an output voltage and an output current, and recognizes a drive frequency, which minimizes the impedance, by sweeping the drive frequency of a drive signal to be a resonance frequency. The drive frequency is swept three times, and the resonance frequency is obtained each time the sweeping is made. If a change amount among the resonance frequencies is a stipulated value or larger, the blade is judged to be loose.
Additionally, the ultrasonic operation system of Patent Document 6 detects a crack of a probe. Namely, this ultrasonic operation system can obtain a resonance frequency from impedance similar to the ultrasonic operation system of Patent Document 5. This system sweeps a drive frequency twice with different excitation currents, obtains a resonance frequency each time the sweeping is made, and judges that a crack occurs in the probe if the resonance frequency in a low excitation current is lower than that in a high excitation current.
The ultrasonic operation apparatuses of Patent Documents 1 to 4 judge an abnormality in a PLL control. Namely, the apparatuses can detect an abnormality only when a drive signal is output to a hand piece, and cannot detect an abnormality except when an output is made. The ultrasonic operation systems of Patent Documents 5 and 6 can also detect an abnormality except when an output is made, but they must perform an impedance calculation, a comparison arithmetic, etc., leading to the complexity of the systems.    Patent Document 1: Japanese Published Unexamined Patent Application No. 2000-287989    Patent Document 2: Japanese Published Unexamined Patent Application No. 2001-258089    Patent Document 3: Japanese Published Unexamined Patent Application No. 2002-186901    Patent Document 4: Japanese Published Unexamined Patent Application No. H7-313937    Patent Document 5: Japanese Published Unexamined Patent Application No. 2002-224134    Patent document 6: Japanese Published Unexamined Patent Application No. 2003-610